The present invention generally relates to copiers or printers. More particularly, the present invention relates to such devices using a thermally applied toner image system.
In printing or copying machines which operate according to the transfer printing principle, be it according to the principle of electrophotography, ionography or magnetography, a toner image is produced on a recording substrate comprising single sheets or endless paper, using a printing device, and this toner image is then thermally fixed in a thermofixing station.
An electrophotographic printing device of this type for endless paper, having a thermal print fixing station, is known from WO 91/09352.
In printing or copying machines of this type, the recording substrate and the toner image fixed upon it, after leaving the fixing station, have a temperature in the range from 90.degree. to 120.degree. or higher, depending on the material property of the recording substrate, which generally comprises paper. In this temperature range, the toner is still in a tacky state. In the case of endless paper printers, the paper web, after it has left the fixing station, runs directly into a post-processing system or it is subsequently directly stacked up in a stacking device.
Now, during stacking it occurs that the printed image sides with their toner images lie on one another and thus also the one toner image of the one side lies on the toner image of the other side. If the temperature of the paper and hence of the toner image is still more than 60.degree. after stacking, adhesion of the printed images lying on one another can occur.
When separating the sheets lying on one another (adhering toner images), disturbing print damage then occurs.
In order to avoid this adhering of the toner images, it is known from DE-A1 39 34 770 to arrange a blower in the region of the stacking device of an electrophotographic printing device, which blower, via an air stream which runs perpendicular to the paper transport direction, flows through the stack and cools the lather.
Furthermore, from JP-A-3-174570 (Patent Abstract of Japan P-1268, 28.10.91, Vol. 15, No. 424), an image-producing device is known, having a thermal print fixing station composed of a fixing roller and a nip roller. Arranged downstream of the fixing station is a thermal converter device with an associated electrical generator, which has a thermal transmission surface with a vaporizer. The residual heat of the transfer medium is removed via the thermal transmission surface and warms a heating medium in the vaporizer, the heating medium flowing through a turbine which drives a generator. The thermal converter or generator serves for the purpose of charging up a storage battery, in order in this manner to save the energy necessary for driving the image-producing device.
In JP-A-54-74444 (Patent Abstract of Japan E-130, 15.08.79, Vol. 3, No. 96), a description is given of a thermal fixing station for an electrophotographic copying machine, which has a heating plate over which the recording substrate is guided and which serves for the purpose of melting the toner on the recording substrate. In order that the heating plate comes into close contact with the recording substrate, a blower is arranged opposite the heating plate, the said blower pressing the recording substrate against the heating plate via an air stream.
In the case of rapid data printers operating in accordance with the principle of electrophotography, which operate in the uppermost printing speed range with a paper transport speed of up to 1 m per second and more, it is becoming more and more problematic to cool the paper, in the short interval between leaving the fixing station and stacking, to a temperature of 60.degree., that is to say the paper web must be cooled by about 60.degree. Kelvin in about 0.5 second. This means a power dissipation of about 4000 W in 0.5 second. Since the thermal transfer between air add paper is only very poor, a correspondingly high air volume must be brought into contact with the paper surface in the short time and must also be specifically guided away again. This correspondingly requires blowers of high air volume with high noise development and large installation size. In addition, the air velocity must be correspondingly high, in order to bring a reasonably large part of the air volume into contact with the paper surface. This can lead to fluttering movements of the recording substrate, which have a disturbing effect during the stacking process.
It is an object of the invention to provide a printing or copying machine having a thermofixing arrangement, in which the recording substrate, after leaving the fixing device, is carefully and effectively cooled with low noise.